The maps showing the Earth's ancient climate were made by mapping the past
positions of the continents (see Methods for more info on
how this is done) and plotting on these maps the distribution of rock types that form
in specific climatic belts. Certain types of rocks, such as coals, which need
abundant rainfall, form under certain climatic conditions (for example, coal forms in
tropical rainforests or temperate forests). The diagram below indicates which
rock types form in which climatic belts. By mapping the past distribution of thousands of
these rock types, we have begun to map the distribution of the ancient climatic belts.

Information on the distribution of climatically sensitive rock types was collected
by A. J. Boucot (U. of Oregon) with help form Chen Xu (Nanjing University).